1. Field of the Invention:
This invention relates to decanting centrifuges for processing liquid material contained in sample tubes. More particularly, the invention relates to centrifuges for separating liquid material contained in sample tubes supported on a spinning rotor into a dense fraction and a supernatant fraction and then decanting the supernatant fraction from the sample tubes while the sample tubes are still being supported on the spinning rotor. (Proposed classification: 233-26).
2. Prior Art:
Centrifuges of the above kind are disclosed in, for example, GB Pat. No. 1,211,942, U.S. Pat. No. 3,401,876 and U.S. Pat. No. 4,285,463. They are commonly used for washing blood cells in connection with the so-called Coombs' test or similiar blood treating operations. Normally, several blood samples are treated simultaneously in different sample tubes supported on the centrifuge rotor.
Coombs' test requires that a sample consisting essentially of red blood cells be repeatedly washed in saline. Each washing cycle includes centrifugal separation of the contents of each sample tube into a denser blood cell fraction and a lighter or supernatant saline fraction containing material washed off from the red blood cells and decantation of the supernatant fraction from the sample tube.
During the separation step the sample tubes are oriented such that the open end or mouth of the sample tubes is substantially closer to the vertical axis of rotation of the rotor than is the opposite bottom end so that the blood cells are collected at the bottom end. In the prior art centrifuges the decantation is accomplished by raising the sample tubes from an inwardly and upwardly inclined position to a substantially vertical position, the supernatant fraction being discharged through the upwardly directed open end of the sample tubes under the influence of the centrifugal force while the blood cell fraction is retained.
During the decanting step it is required to discharge the supernatant fraction as completely as possible while avoiding loss of the red blood cells--which occupy a very small volume--with the decanted supernatant. This requirement is not met in a satisfactory manner in the prior art centrifuges.